Catalytic action of metallic salts in autoxidation and polymerization. IV. Polymerization of methyl methacrylate by cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide or dioxane hydroperoxide

Polymerization of methyl methacrylate was carried out by four initiating systems, namely, cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide (t-Bu HPO) or dioxane hydroperoxide (DOX HPO). Dioxane hydroperoxide systems were much more effective for the polymerization of methyl methacrylate than tert-butyl hydroperoxide systems, and cobaltous acetylacetonate was more effective than cobaltic acetylacetonate in both hydroperoxides. The initiating activity order and activation energy for the polymerization were as follows: Co(acac)₂–DOX HPO (E_a-9.3 kcal/mole) > Co (acac)₃–DOX HPO (E_a = 12.4 kcal/mole) > Co(acac)₂–t-Bu HPO (E_a = 15.1 kcal/mole) > Co(acac)₃–t-Bu HPO (E_a-18.5 kcal/mole). The effects of conversion and hydroperoxide concentration on the degree of polymerization were also examined. The kinetic data on the decomposition of hydroperoxides catalyzed by cobalt salts gave a little information for the interpretation of polymerization process.     

Catalytic Action of Metallic Salts in Autoxidation and Polymerization. VII. Polymerization of Methyl Methacrylate by Cobalt(ll) or (III) Acetylacetonate-Dioxane Hydroperoxide

Abstract

Polymerization of methyl methacrylate by Co(II or III) acetylacetonate-dioxane hydroperoxide [abbreviated as Co(acac)2, Co(acac)₃, and DOX HPO, respectively] was carried out in dioxane solvent, and the differences in polymerization rate and the degree of polymerization between two initiating systems were compared. Co(acac)₂-DOX HPO for the initiation of the polymerization system was more effective than Co(acac)₃-DOX HPO. The polymerization rate equations for both initiating systems obtained from kinetic data were as follows. For Co(acac)₂-DOX HPO initiating system: R_p=k [M]^3/2[Co(acac)₂]^1/7[DOX HPO]^?     

Determination of cyclo C6 and C7 peroxides and hydroperoxides by gas chromatography

Summary A method for determining cyclo C₆-C₇-peroxides and hydroperoxides by high-resolution capillary GC has been developed. The compounds were synthesized in the liquid phase and identified in chromatograms of the reaction mixture of cyclohexyl hydroperoxide and cycloheptane using GC-MS. Peroxy compounds were determined using an FID. The effective carbon number (ECN) concept was used to calculate response factors of the peroxy compounds analysed. The experimentally determined response factor for cyclohexyl hydroperoxide was identical (within error limits) with that calculated.     

Origin of byproducts during the catalytic autoxidation of cyclohexane

The formation of byproducts during the Co(acac)2 and Cr(acac)3-catalyzed cyclohexane autoxidation is compared with the noncatalyzed thermal process. CoII ions seem to cause only a moderate perturbation of the reaction mechanism, causing a fast conversion of the cyclohexyl hydroperoxide via a redox cycle, rather than via abstraction of the alphaH-atom by chain carrying peroxyl radicals. Nevertheless, both the radical propagation and the CoII-induced decomposition of the hydroperoxide cause the formation of cyclohexoxy radicals that are partially transformed to 6-hydroxyhexanoic acid, the major primary byproduct for these systems. However, during the CoII-catalyzed reaction, the concentration of cyclohexanone increases much faster than that of the hydroperoxide, causing the ketone to take over the role of dominant byproduct source. A mechanism for the conversion of cyclohexanone to ring-opened byproducts is put forward. Cr(acac)3 seems to catalyze additional reactions, some of them probably leading directly to byproducts. Indeed, the evolution of (by)products is significantly different from the CoII-catalyzed and the thermal systems, in the sense that they all seem to be primary in origin.     

Kinetics of epoxidation of 2-methyl-2-pentene

The kinetics of epoxidation of 2-methyl-2-pentene with cumene hydroperoxide catalyzed by MoO₂ (acac)₂ has been studied in the temperature range of 35–65°C. The observed kinetic behavior is consistent with the formation of a hydroperoxide-catalyst complex and a simple competitive inhibition step, involving the formation of an inactive epoxide-catalyst complex. The reaction parameters have been calculated.     

Catalytic epoxidation of C6-alkenes. Determination of the relative reactivity ratios

The relative reactivity ratios R_i for eleven C₆-alkenes interacting with cumene hydroperoxide in the presence of MoO₂(acac)₂ have been determined at 323K and at different mole ratios of the reactants by the method of competitive reactions.     

Manganese(II) β-diketonate catalyzed oxidation of cyclohexane bytert-butyl hydroperoxide

Oxidation of cyclohexane bytert-butyl hydroperoxide was carried out in acetonitrile solution at room temperature in the presence of manganese(II) β-diketonate complexes, Mn(acac)₂, Mn(acac)₂.2H₂O, Mn(ba)₂.H₂O, Mn(dbm)₂ and Mn(dbm)₂.2H₂O (where acacH=acetylacetone, baH=benzoylacetone and dbmH=dibenzoyl-methane). Cyclohexanol and cyclohexanone were obtained as the products. Oxidation ofcis-cyclooctene gave the corresponding epoxide together with two minor byproducts in the presence of Mn(acac)₂.2H₂O and Mn(dbm)₂.2H₂O. A mechanistic pathway predominantly involving autoxidation is proposed. IPCL communication No. 322     

Effect of acetonitrile on the catalytic decomposition of hydrogen peroxide by vanadium ions and conjugated oxidation of alkanes

The rate of hydrogen peroxide decomposition in acetonitrile in the presence of a vanadate anion and pyrazine-2-carboxylic acid decreases remarkably when alkane (cyclohexane, n-heptane, isooctane) is added to the reaction solution. The alkane added is oxidized by this system to alkyl hydroperoxide. This is explained by the fact that much more hydrogen peroxide molecules are consumed to acetonitrile oxidation with formation of the final products, which is suppressed considerably by additives of necessary amounts of alkane, than those consumed to the oxidation of cyclohexane to form cyclohexyl hydroperoxide. In an organic solvent, H₂O₂ decomposes in a non-chain radical process.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2231–2234, October, 2004     

Rh-Catalyzed Oxidation of Anthracenes with tert-Butyl Hydroperoxide. Kinetic Aspects

The polar effects of substituents on reactivity in oxidation of 2-substituted anthracenes with tert-butyl hydroperoxide (TBHP)/Rh(PPh₃)₃Cl have been investigated and compared with those obtained with TBHP/VO(acac)₂ and chromic acid. The anthracene reactivities obtained from competition experiments are correlated with Hammett's σ_p-constants. The P-values are -2.60 for chromic acid and 0.72 for TBHP/VO(acac)₂. A poor correlation with p = ?0.17 (r = 0.756) was obtained for TBHP/Rh (PPh₃)₃Cl. It is concluded that the Rh-catalyzed reaction does not consist in electrophilic oxygen transfer to the anthracene.     

Redox kinetics of metal complexes in nonaqueous solutions. V. Kinetics and mechanism of the iron (II) reduction of the acetylacetonates of manganese (III) and cobalt (III) in acetonitrile

The electron transfer step of the reduction of Mn(acac)₃ and Co(acac)₃ by Fe(II) in acetonitrile is preceded by the one-ended dissociation of an acac ligand and the formation of a binuclear bridged complex. After the electron transfer has taken place through the bridging ligand, the complex dissociates into the products M(acac)₂ (M = Mn, Co) and Fe(acac)²⁺. These primary reaction products could not be identified, since the transfer of acac from M(acac)₂ to Fe(acac)²⁺ is too rapid, producing ultimately Fe(acac)₃ and M²⁺. The M(III)-oxygen cleavage is accelerated by M(acac)₂. Furthermore, the dissociation of the binuclear intermediate is catalyzed by the M(acac)₃ reactant. Mn(acac)₃ is reduced more than a thousand times faster than Co(acac)₃.     

Mechanism of the selective formation of cyclohexanone in the decomposition of cyclohexyl hydroperoxide by chromium stearate

From a comparison of the rates of formation of cyclohexanone and 2-decanone in cyclohexane solutions of cyclohexyl hydroperoxide or tert-butyl-hydroperoxide in the presence of chromium(III) stearate and a mixture of cyclohexanol and 2-decanol in an atmosphere of argon at 350 K, it is concluded that the direct breakdown of cyclohexyl hydroperoxide by chromium stearate leads to selective formation of cyclohexanone. The contribution of the oxidation of cyclohexanol to ketone formation at a cyclohexanol concentration comparable with the hydroperoxide concentration (0.1 M) is 10%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2239–2242, October, 1991.     

The Dual Function of PhOH Included in the Coordination Sphere of the Nickel Complexes in the Processes of Oxidation with Dioxygen

The role of ligands in the regulation of the catalytic activity of Ni-complexes (Ni(acac)₂) in green process-selective ethylbenzene oxidation with O₂ into α-phenyl ethyl hydroperoxide is considered in this article. The dual function of phenol (PhOH) included in the coordination sphere of the nickel complex as an antioxidant or catalyst depends on the ligand environment of the metal. The role of intermolecular H-bonds and supramolecular structures (AFM method) in the mechanisms of selective catalysis by nickel complexes in chemical and biological oxidation reactions is analyzed.     

(−)-Fenchone derived epoxy alcohols—preparation and configuration

Several chiral diastereoisomerically pure epoxy alcohols were prepared diastereoselectively in high yields after epoxidation of allyl and homoallyl alcohols containing the 1R-fenchone skeleton with VO(acac)₂/t-butyl hydroperoxide. The configurations of some of the new chiral compounds were determined by NMR methods. An interesting rearrangement reaction of an epoxy alcohol to an olefinic diol catalyzed by V⁵⁺ ions was observed.     

Synthesis and Structure of a Series of New Molybdenum(VI) Complexes with the Esters of 2‐Mercaptonicotinic Acid

The novel dioxomolybdenum(VI) complexes with methyl ( 1 ), ethyl ( 2 ), n‐propyl ( 3 ), i‐propyl ( 4 ), n‐butyl ( 5 ) and cyclohexyl ( 6 ) ester of 2‐mercaptonicotinic acid have been prepared in the reactions of MoO₂Cl₂ and MoO₂(acac)₂ (acac = 2,4‐pentandionate) with mercaptonicotinic acid in corresponding alcohol. The esterification reaction was catalyzed by Mo^V originated from the reduction of Mo^VI with mercaptonicotinic ‐SH group with simultaneous formation of S–S bond resulting from the condensation of two 2‐mercaptonicotinic molecules. The presence of Mo^V was proved by ESR spectra. The molecular and crystal structures of 1 , 2 , 3 and 4 as well as of the by‐products 1,1′‐dithio‐2,2′‐n‐butylnicotinoate ( 7 ) and tetramethylammonium hexachloromolybdate(V) ( 8 ) have been determined by a X‐ray single crystal diffraction. The complexes 1 – 4 contain MoO₂²⁺ core with octahedral coordination of each molybdenum atom complexed by two 2‐mercaptonicotinato N and S donor atoms.     

微波辐射下氧化N-烷基酰胺合成二酰亚胺

二酰亚胺是一个很有用的官能团, 它广泛存在于天然产物和有药物活性的分子中. 通过微波辐射条件合成它吸引了很多化学家的注意. 极性反应物可以吸收微波辐射, 化学家将微波应用于一些化学反应中. N-烷基酰胺(NH邻位有一个亚甲基CH₂)和N上没有取代的内酰胺可以被过氧化物和过渡金属盐氧化成二酰亚胺. 报道了在乙酸乙酯中过氧叔丁醇和乙酰丙酮锰(III)在微波条件(90 W, 5 min)下, 酰胺迅速、高选择性地、高产率地转变为二酰亚胺的方法.     

Glyoxal-promoted homogeneous catalytic oxygenation of cyclohexane with hydrogen peroxide in the presence of V and Co compounds

The efficiency of cyclohexane oxidation with hydrogen peroxide catalyzed by vanadyl acetylacetonate at 40 °C and atmospheric pressure is enhanced by glyoxal additive. The process selectively produces a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone with a high rate (up to 4400 catalyst turnover number). Cobalt(II) acetylacetonate is much less active but more selective with respect to cyclohexyl hydroperoxide.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 307–310, February, 2005.     

Hydrolysis and Polymerization of Dimethyldiethoxysilane, Methyltrimethoxysilane and Tetramethoxysilane in Presence of Aluminum Acetylacetonate. A Complex Catalyst for the Formation of Siloxanes

Hydrolysis and polymerization of dimethyldiethoxysilane (DMDE), methyltrimethoxysilane (MTMS) and tetramethoxysilane (TMOS) in the presence of aluminum acetylacetonate (Al(acac)₃) have been investigated by infrared and NMR spectroscopy. In the absence of acidic catalyst, Al(acac)₃ catalyzes the hydrolysis of all the silanes. The catalytic activity of Al(acac)₃ is less than that of HNO₃, but larger than that of NH₃. The hydrolysis rate increases with increasing concentration of Al(acac)₃ in DMDE. The hydrolysis of TMOS occurs rapidly after an inductive period, which becomes longer with addition of Al(acac)₃. The results are explained by assuming an Al(acac)₃ catalyzed hydrolysis and a silanol catalyzed hydrolysis. The addition of Al(acac)₃ causes changes in polymerization of the resultant silanols. In DMDE and MTMS, it stabilizes the silanols at the early stage, and then enhances their polymerization. The polymerization in TMOS leads to the formation of precipitates that have a high degree of polymerization. The polymerization appears to proceed via a deprotonation mechanism including transfer of protons from silanols to Al(acac)₃. The present results strongly suggest that, besides acids and bases, metal complexes can be used as catalysts for the formation of siloxanes under ambient conditions.     

The polarographic and voltammetric behaviour of acetylacetonato and hexafluoroacetylacetonato complexes in acetonitrile

The polarographic behaviour of Ce(acac)₄, Ce(acac)₃, Eu(acac)₃, Fe(acac)₃, Cr(acac)₃, Co(acac)₃, Mn(acac)₃, NaMn(acac)₃, Mn(acac)₂, Ni(acac)₂, Cu(acac)₂, VO(acac)₂, Fe(hfacac)₃, Cr(hfacac)₃ and Cu(hfacac)₂ has been studied in acetonitrile on the dropping mercury electrode. Half-wave potentials versus bisbiphenylchromium(I)/(0), the reversibility of the electrode reaction and the number of electrons participating in the electrode processes measured by coulometry are reported. Cyclovoltammetric measurements have been performed on the hanging mercury drop electrode and on the stationary platinum electrode, the data of these studies are given. quite different behaviour has been observed on the platinum electrode compared to the dropping mercury electrode. Large scale electrolysis was employed to obtain information on the reaction products. The influence of the electrode material and the reaction mechanisms are discussed.     

Solvent and salt effects on the redox behaviour of trisacetylacetonato manganese(III)

The polarographic and voltammetric behaviour of trisacetylacetonato manganese(III) [Mn(acac)₃] has been studied in methanol, ethanol, tetrahydrofurane, butyrolactone, propylenecarbonate, N,N-dimethylformamide, acetonitrile, nitromethane, N-methylpyrrolidone(2), 1,2-dichloroethane, dichloromethane, dimethylsulfoxide and acetic acid, Mn(acac)₃ was found to undergo a reversible one-electron reduction to Mn(acac)₃^? in most of the solvents mentioned. A further reduction at very negative potentials has been also observed in several solvents. The oxidation of Mn(acac)₃ to Mn(acac)₃⁺ has been studied by cyclovoltammetry in dichloromethane, nitromethane, acetonitrile, propylenecarbonate, N-methylpyrrolidinone(2), N,N-dimethylformamide and dimethylsulfoxide. The polarographic behaviour of NaMn(acac)₃ and Mn(acac)₂ has been investigated in the seven solvents listed above as well as in methanol. The half-wave potentials and the peak potentials referred to bisbiphenylchromium(I)/bisbiphenylchromium(0) as a reference redox system were found to vary with the nature of the solvent. Conductivity studies of Mn(acac)₃ and NaMn(acac)₃ have been carried out in these solvents. U.v.-visible and near i.r. spectra have been recorded of Mn(acac)₃, NaMn(acac)₃, Mn(acac)₂ and Na(acac) in the solvents mentioned. It has further been observed that the half-wave potentials for the polarographic reduction of Mn(acac)₃ shifted to more positive values by the addition of alkali metal ions and to more negative values by the addition of halide ions. The interactions of the solvent with Mn(acac)₃ and the variation of redox potentials with both the solvent and the added electrolytes will be discussed.     

Mechanism of cyclohexane oxidation by molecular oxygen in the biomimetic iron porphyrin system with proton and electron donors: II. A molecular pathway

The kinetics of the accumulation of cyclohexyl hydroperoxide, alcohol, and ketone during cyclohexane oxidation in an O₂/FeP/AcOH/Zn/CH₃CN biomimetic system is studied by gas-liquid chromatography. The factors determining the selectivity of the nonradical oxidation pathway, which results in the formation of more than 80% of the products, are considered. A scheme of the molecular pathway of alcohol and ketone formation is proposed, which agrees well with the experimental data. The kinetic parameters for cyclohexane oxidation catalyzed by iron porphyrins with various substituents in the phenyl rings in this system with and without an electron carrier (methylviologen) are calculated.